Dry bag soft luggage recommendations.

[Chicken Chaser]

I'm after something to fulfil the requirement of a couple of camping weekends away on the bike. I've seen the Givi 40l dry bags which look good but I seem to have seen somewhere that there was one with a zip on it once rolled down for ease of use.
Anyone recommend a fairly lost cost option? I've got a tankbag and some ultra light camping gear so something in the 40-60l range would be ideal.